1. Field of the Invention
The invention relates to the field of the methods for changing rolls in a roll stand, and to that of rolling installations implementing such methods.
2. Description of Related Art
When a working roll in a roll stand is worn or damaged, it must be changed. To do so, the rolling mill is stopped and the roll to be replaced is unloaded from the stand. It is then led towards a workshop dedicated to rolls for rectification purposes. Once the stand has been unloaded, a new roll is loaded into the empty stand and the operation of the rolling installation is resumed.
More particularly, the invention applies to rolling mills for which the working rolls are not directly driven into rotation, but by means of back-up rolls, which are driven into rotation by associated driving means, and drive in turn by friction the working rolls in contact with the product to be rolled. Such is the case for example in a “skin-pass” rolling mill intended for conferring to a band to be rolled a particular surface finish. Thus, for such rolling mills, the engine side of the roll stand (the side where the driving means are situated, in opposition to the operating side) is relatively clear, at least in the vicinity of the working rolls.
It is then possible to elect either an installation enabling to unload the worn rolls on the engine side, or an installation enabling to load new rolls from the engine side.
According to a first known method enabling to extract a worn roll from the stand while inserting a new roll inside the stand, the rolling installation is fitted with a pushing displacement device. The actuation of this device enables to push a new roll in order to load it inside the stand. The new roll pushes in turn the worn roll initially in the stand in order to unload it outside the stand.
Thus, the new roll is located initially, before being loaded in the stand, on a first side of the stand where the pushing device is situated, and the worn roll is received on a carriage arranged on the other side of the stand with respect to the pushing device.
It will be noted that the pushing device may be situated either on the engine side or on the operating side.
According to this first known method, the pushing device is a kind of simple piston which applies, by contact on one end of the new substitute roll, a pushing load directed along the axis of this new roll. The new roll is first moved, then brought in contact with one end of the worn roll to be replaced. In turn, the new roll applies a contact load to the worn roll, along the axis of this worn roll and capable of pushing the worn roll, in order to extract it outside the stand.
A shortcoming of this first method known lies in that it should be carried out very slowly so that, at any time, the rolls never acquire too great inertia which would render their movements uncontrollable. It is also necessary that the different contact reaction loads are perfectly aligned with the axis of the rolls so that the latter move axially along a loading direction of the stand. In the reverse case, the rolls, the bearings or the chocks wherewith the various rolls are fitted, or still other parts of the stand might be damaged.
According to a second known method, the rolling installation is fitted with a pull-type displacement device. Then one end of the worn roll in the stand has been fastened to one end of the new roll outside the stand, when the pulling device grips the other end of the worn roll to be replaced. The pulling device then applies a tensile load capable of moving the worn roll outside the stand. In turn, the worn roll drives by traction the new roll inside the stand. The worn roll extracted from the stand is received on a carriage arranged on the same side as the pulling device, whereas the new roll has been located previously, before being loaded in the cage, on the other side of the installation, opposite to the side where the pulling device is situated. It will be noted that one may elect to locate the pulling device either on the engine side or on the operating side.
According to this second known method, the fastening of the pulling device to one of the ends of the worn roll inside the stand, as well as the fastening of the other end of the worn roll to one of the ends of the new roll outside the stand, may be realised by co-operation between a hook and a ring. For instance, when the pulling device is fed towards the worn roll, the ring carried by the pulling device, by coming in contact with the hook, carried by the corresponding end of the worn roll, starts to be lifted by rotation around a pivot pin. Once the ring has cleared the tip of the hook, recall means lower it automatically inside the loop formed by the hook. Possibly, a collapsible finger is then actuated to close the hook around the ring and to prevent the latter from being dislodged. The rolls may then be moved by traction.
A difficulty of such known method lies in that after inserting new rolls in the stand, it is necessary to conduct a complex and time-consuming operation in order to disengage the hooks from the corresponding rings. Moreover, such operation is generally carried out manually by an operator.